You can expect to get around from 2hrs (DVD viewing) to 3hrs (web browsing) battery life with the standard 6 cell battery.
As long as you're still playing the same games 7yrs from now you should do OK for longevity.
I thought laptop batteries lasted longer nowadays. Well, I can't forsee playing the same games that long from now. As far as the 5650+ laptops you mentioned are concerned, is there a big difference between the Lenovo and the HP's performance?
Also is Levono a respectable brand, or are they known for poor craftsmanship- I've never had an experience with them.